Merge pull request #387 from Earlopain/false-negative-string-identifi…

…er-argument

Make `Performance/StringIdentifierArgument` aware of string interpolation

changelog/fix_a_false_negative_for_string_identifier_argument.md

@@ -0,0 +1 @@
+* [#386](https://github.com/rubocop/rubocop-performance/issues/386): Fix a false negative for `Performance/StringIdentifierArgument` when using string interpolation. ([@earlopain][])

lib/rubocop/cop/performance/string_identifier_argument.rb

@@ -16,11 +16,13 @@ module Performance
       #   send('do_something')
       #   attr_accessor 'do_something'
       #   instance_variable_get('@ivar')
+      #   const_get("string_#{interpolation}")
       #
       #   # good
       #   send(:do_something)
       #   attr_accessor :do_something
       #   instance_variable_get(:@ivar)
+      #   const_get(:"string_#{interpolation}")
       #
       class StringIdentifierArgument < Base
         extend AutoCorrector
@@ -45,22 +47,34 @@ class StringIdentifierArgument < Base
           respond_to? send singleton_method __send__
         ] + COMMAND_METHODS).freeze
 
+        # rubocop:disable Metrics/CyclomaticComplexity
         def on_send(node)
           return if COMMAND_METHODS.include?(node.method_name) && node.receiver
           return unless (first_argument = node.first_argument)
-          return unless first_argument.str_type?
+          return unless first_argument.str_type? || first_argument.dstr_type?
 
           first_argument_value = first_argument.value
           return if first_argument_value.include?(' ') || first_argument_value.include?('::')
 
-          replacement = first_argument_value.to_sym.inspect
+          replacement = argument_replacement(first_argument, first_argument_value)
 
           message = format(MSG, symbol_arg: replacement, string_arg: first_argument.source)
 
           add_offense(first_argument, message: message) do |corrector|
             corrector.replace(first_argument, replacement)
           end
         end
+        # rubocop:enable Metrics/CyclomaticComplexity
+
+        private
+
+        def argument_replacement(node, value)
+          if node.str_type?
+            value.to_sym.inspect
+          else
+            ":\"#{value.to_sym}\""
+          end
+        end
       end
     end
   end

spec/rubocop/cop/performance/string_identifier_argument_spec.rb

@@ -19,9 +19,14 @@
       RUBY
     end
 
-    it 'does not register an offense when using interpolated string argument' do
-      expect_no_offenses(<<~'RUBY')
-        send("do_something_#{var}")
+    it 'registers an offense when using interpolated string argument' do
+      expect_offense(<<~RUBY, method: method)
+        #{method}("do_something_\#{var}")
+        _{method} ^^^^^^^^^^^^^^^^^^^^^ Use `:"do_something_\#{var}"` instead of `"do_something_\#{var}"`.
+      RUBY
+
+      expect_correction(<<~RUBY)
+        #{method}(:"do_something_\#{var}")
       RUBY
     end
   end